1. Field of the Invention
The present invention relates to a built-in type stereo microphone unit adapted to be installed in a video camera or the like where sound is recordable in a stereophonic mode.
2. Description of the Prior Art
For processing input sound in a stereophonic mode, it is customary to prepare two unidirectional microphones 300 as illustrated in FIG. 6. Such two microphones 300 are so disposed that the sound receiving directions thereof form an angle .theta. (ranging from 90.degree. to 130.degree.) and also that the sound receiving positions thereof are spaced apart from each other by a distance greater than 15 cm.
The unidirectional microphone 300 generally has such directivity characteristic as represented by a plot P in FIG. 7, and the plot P is obtained when the microphone 300 is disposed at a center O.
As will be understood from FIG. 8 also, if each microphone 300 is used incorporated in a microphone capsule 300A, the characteristic shown in FIG. 7 is achieved upon mutual combination of sound waves A and B emitted from a sound source and received at the front and the back of the microphone capsule 300A.
It is therefore necessary to ensure, behind the microphone capsule 300A, a sufficient space without any impediment or reflective surface so as to avert a phenomenon that the sound waves from the sound source are reflected as denoted by C and then are received by the microphone 300.
There may be contrived a technique of performing a stereophonic recording operation by the use of two nondirectional microphones each having such directivity characteristic as represented by a plot Q in FIG. 9, but such technique is not employed in general.
However, if unidirectional microphones 300 are installed in a casing of a small-sized video camera for example, a sufficient space is not existent around microphone capsules 300A to permit execution of a stereophonic recording operation. Therefore it is customary that one-point stereo microphones are provided in a posture projecting outward from the casing.
Since restriction is unavoidable with respect to dimensional reduction of a video camera and the degree of freedom in design and so forth, it has been urgent heretofore to realize development of superior microphones which are adapted to be installed in a casing and are still capable of performing a stereophonic sound processing operation.